A Split Vote on Alternative Electoral Systems

My print column this week examines the debate over voting systems that theorists and reformers have backed to replace the system prevalent in the U.S. and many other places, in which each voter gets one vote and the candidate with the most votes wins. Among possible alternative systems include some where voters rank candidates and others where they assign candidates scores.

Instant runoff, the focus of my column, has gotten the most traction so far. But some mathematicians point out that the system could give rise to various troubling results. Two significant ones: Voters who decide to shift their support from one candidate to a second can hurt that second candidate; and voters can get a worse outcome if they choose to show up to the polls, inadvertently helping their least-favorite candidate (the no-show paradox). Robert Z. Norman, Dartmouth College professor emeritus of mathematics, has simulated three-candidate elections in which each candidate has at least 25% of support and finds that each of these apparent paradoxes occur about one in five times.